1. Field of the Invention
The present invention generally relates to a hand tool, and more particularly to a tool for making precise rotational adjustments to electrical or mechanical devices.
2. Description of Related Art
Many small electronic components, such as potentiometers or variable resistors, are adjusted by turning a tiny dial or screw. The dial typically includes an exposed slot or socket which receives the end of a common flat-blade jeweler's screwdriver or similar driving tool to rotate the dial. Turning the dial commonly changes the resistance of a potentiometer, or tunes the frequency of a crystal oscillator.
In the past, adjustment dials on such electronic components commonly were "multi-turn" dials. It required several complete revolutions of the dial to traverse the complete range of adjustability of the component. For instance, the range of adjustment of 1 to 60 ohms resistance in a potentiometer would correspond to three complete turns of the adjustment dial. Small movements of the multi-turn dial produce small changes in the component's characteristics, and large changes require several complete turns. Multi-turn dials thus generally are easily adjusted using a common jeweler's screwdriver.
The present trend in the electronics industry toward smaller electronic components, however, has made the multi-turn dial less attractive. Multi-turn dials require more complex mechanisms than single-turn dials, and thus cannot be packaged as compactly as the single-turn dial components. The direction in the electronics industry thus appears headed toward single-turn adjustment dials.
A single-turn dial spans the complete range of a component's electronic characteristics in a single revolution, and small movement of the dial produces large changes in the electronic characteristic (e.g., resistance) in the component. As a result, it is very difficult to adjust a single-turn components by hand using a screwdriver.
Several prior screwdrivers have been developed to assist technicians to adjust or assemble small electronic and mechanical components. Such tool have commonly included a handle and driving blade similar to that of a common screwdriver. Unlike a conventional screwdriver, however, a portion of the handle function as a tumbler that is coupled to the blade via a reducing gearset (e.g., a planetary gearset). U.S. Pat. No. 4,048,874 issued to Riches discloses an example of a prior screwdriver.
Although these types of screwdrivers reduce the rotation of the blade relative to the rotation of the handle tumbler, such screwdrivers tend to be difficult to use. Because of the commonly co-axial location and orientation between the handle tumbler and the tool blade, such devices generally must be used with two hands: one hand to hold steady the handle, and the other to rotate the tumbler. The user must hold the tool steady because the gear friction commonly is greater than the friction in the dial or screw of the electrical or mechanical device being adjusted. Using two hands, however, commonly obscures the work area from view. It also inhibits use of the tool in confined areas.
In addition, such tools tend to be overly complicated, involving complex gear trains. For instance, the screwdriver disclosed by U.S. Pat. No. 4,048,874 teaches the use of a planetary gear train to reduce the rotation speed of the screwdriver blade relative to the rotation of the handle tumbler. The complex structure of prior designs make such tools expensive and prone to breakage.